A solid oxide fuel cell (SOFCs) is a type of fuel cell which reacts a fuel gas with an oxidant to generate DC electric current. SOFCs may have an anode, an electrolyte and a cathode, and have been made from a variety of materials and in a variety of geometries. Fuel processing is required to render hydrocarbon fuels (such as propane, butane, etc.) suitable for SOFCs. For example, known designs for fuel processors include those done with a separate external reactor where a catalytic substrate processes a hydrocarbon fuel such as butane (C4H10), propane (C3H8) or diesel fuel (JP-8 or JET-A) to a suitable fuel gas such containing carbon monoxide (CO) and hydrogen (H2). CO and Hydrogen gas are then oxidized at an active area of a SOFC to carbon dioxide and water, with DC current generated. Non hydrocarbon fuels such as ammonia (NH3) can also be transformed into SOFC fuel using one or more catalytic reactions.
Current collectors are used on known SOFCs to collect electric current generated by the fuel cell. Good electrical conductance is important for increasing recovery of the electrical energy generated by the fuel cell. However, the harsh environment of a fuel cell can make current collection difficult. Fuel cell current collectors must be chemically and thermally robust, as they are exposed to oxidative stresses, reductive stresses, and operating temperatures in the range of about 600-950° C. Known current collectors used in tube-shaped SOFC designs include the so-called “Westinghouse” design where a strip of a lanthanum-chromite ceramic runs along the length of the fuel cell, and a nickel felt electrically connects an electrode of one tube to an electrode of another tube. This design is disadvantageous for several reasons, including the expense of the ceramic, the fact it is a relatively low strength and brittle material, and that each tube must be rigidly connected to its adjacent tube. Portable fuel cell designs can be subject to physical stresses and shocks, etc., and low strength, brittle materials are ill suited for such use.
It has also been known to use silver wires as current collectors, as they are capable of operating in high temperatures and are resistant to oxidation. Known designs have used silver wire wrapped around the cathode of a tubular SOFC in a spiral fashion. Such spiral wires, however, do not make reliable electric contacts as they can move with respect to the tube. This is true even if tightly attached when assembled, as elastically tight fits are relaxed at the high operating temperatures of fuel cells.
It would be desirable to provide a solid oxide fuel cell with a current collector of a simple, lightweight design which is also robust in construction and capable of withstanding thermal cycling and expected physical stresses.